Coherent optical communications systems play an important role in communication transmission networks due to their huge transmission bandwidths, great potential for expansion, extremely low transmission loss and low cost. In coherent optical communication, in order to ensure stable transmission of signals, an effective method is needed in an optical transceiving system to monitor and deal with various state changes of optical fibers in a natural environment, such as bending, jitter, being hit, and the like. Research suggest that monitoring polarization changes is beneficial to quickly response to, analyze of, and repair of such damages by an optical transceiver. That is, it is desirable to accurately reflect state changes of fibers in an optical link by monitoring changes of polarization states of signals in the optical link.
Currently, there are many different ways to monitor polarization states of a signal. A first method is one based on hardware implementation, in which a DC laser and a commercial polarimeter, or two detectors and an optical rotator, are used to monitor changes of polarization states. The second method is based on receiver digital signal processing, which is capable of tracking changes of polarization states in an optical link at a speed faster than the first method.
It should be noted that the above description of the background is merely provided for clear and complete explanation of the present disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of the present disclosure.